The Nakshtras, also called lunar mansions or constellations. In Jyotish or Indian astrology there are 27-nakshatras prescribed by Parasara (ancient sage who founded Vedic astrology).

The first nakshatra, Ashwini, starts at Aries 0’00’’ degrees and ends at Aries 13’30’’.
The next nakshatra, Bharani, starts at Aries 13’20’’ and ends at Aries 26’40’’.
Then Krittika starts at Aries 26’40’’ and ends at Taurus 10’00’’.
Then Rohini from Taurus 10’00’’ to 23’20’’ and so on, until Revati, which extends from Pisces 16’40’’ to Aries 0’00’’

Two nakshatras take up 26’40’’, which is 3’20’’ short of one full sign ( a full sign is 30’00’). Therefore, 3’20’’ is 1/4 of a nakshatra, and is called a nakshatra-pada, or simply a pada(means step). As such, Aries contains Ashwini, Bharani, and the 1st pada of Bharani. Taurus contains padas 2- 4 of Krittika, Rohini, and the first 2 padas of Mrgasira. Each nakshatra therefore contains 9 padas (note that 3’20’’ x 9 = 30 degrees, or one full sign).
The notation Ashwini-1 means the 1st pada of Ashwini, Ashwini-2 the 2nd pada, and so on. Aries then contains Ashwini, Bharani, and Krittika-1, and Taurus contains Krittika-2,3,4, Rohini, and Mgrasira-1,2.

Four signs contain 9 x 4 = 36 padas, or 9 full nakshatras. This happens 3 times, as indicated by the breaks in the nakshatra table below. Aries - Cancer contain Ashwini - Ashlesha, Leo - Scorpio contain Magha - Jyeshta, and Sagittarius - Pisces contain Mula - Revati.
Just like the signs, each nakshatra has a ruler or owner. Unlike the signs, Rahu and Ketu are assigned rulerships. Ashwini is ruled by Ketu, Bharani by Venus, Krittika by Sun, then Mars, Rahu, Jupiter, Saturn, and Mercury. The cycle then repeats in the same order two more times. Note the order of nakshatra rulership is the same as the mahadasa order in the vimshottari dasha scheme, as it must be, since this is how the vimshottari dasha order is defined.
A table summarizing the nakshatras is given below.

The nakshatras act as a filter through which the grahas act. Take Sun at Aries 10-00; this corresponds to Ashwini, which is ruled by Ketu. Sun therefore has an influence from Ketu, and we need to look at the disposition of Ketu to fully understand the influence of Sun.
We continually emphasize the word graha here and in other articles in this web site. It is explained there that the word graha means to grasp, or lay hold of. The entity that the grahas are grasping onto are the nakshatras.

When one graha is in a nakshatra ruled by another graha, it acts to integrate the influences of the two grahas. This integration is often important for providing balance. For example, Jupiter is an expansive graha, and this is taken to be "good". On the other hand, too much expansion can result in obesity, or excessive accumulation. Saturn, on the other hand, indicates constriction, and is often considered "bad". When Jupiter and Saturn balance each other it can provide for a very strong foundation which can result in "healthy growth", or growth (expansion) with balance.

Following table will show certain characteristics of 27 Naksharta
in Vedic Astrology

those that feed on blood + flesh, cruel men, those engaged in killing, imprisoning and beating others, low-born persons, those who are devoid of courage, character or nobility, burial related jobs, menial jobs, dancers, actors, musicians, singers, those who play on musical instruments, the wicked, hunters.

3.

Krittika

Brahmans who maintain and worship the sacred fire daily, those who know of the sacred hymns and sacrificial rules, grammarians, miners, barbers, Brahmans, potters, priests and astrologers, commentators, gold miners, those who work on fire i.e. goldsmiths, blacksmiths etc., army commanders.

sacrifice conductor, ministers, kings, fishermen and the like, virtuous men and those that are engaged in big and small sacrifices, those involved in physical exercise, persons engaged in ringing bells, those who make loud announcements (or those who live in hamlets), gamblers.

men devoted to Indra and Gani, those learned and skilled in handling fire, engineers, merchants.

17.

Anuradha

men of prowess, heads of corporations, friends of the virtuous, lovers of assemblies, tourists (or lovers of carriages), all honest persons in the world, athletes, vehicle repair and sales, ministers, those that work with wheels such as potters, oil-makers etc., those that beat gongs or bell-makers, friends, Kshatriyas.

18.

Jyesta

great battle heroes, those who are noted for pedigree, wealth and fame, thieves, kings intent on conquests and commandants, kings, their preceptors, those that receive royal patronage or honour, leaders of Kshatriyas.

19.

Moola

physicians, leaders of groups, those who deal in flowers, roots and fruits, very wealthy persons, those who live only on fruits and roots, warriors, those who deal in medicinal roots (druggists).

20.

Purva Ashada

tender-hearted people, navigators, wealthy persons, fishermen, the truthful, pure, constructors of bridges/dams/canals, those who live by water, meat seller.

thieves, cowherds, murderous persons, niggards, those engaged in despicable and roguish activities, those devoid of virtuous or religious observances, those clever in single combat, physicians, poets, drunkards, traders, politicians, gamblers.

26.

Uttara Bhadra

Brahmans, those that are engaged in sacrifices, charity and penance, ascetic, very wealthy persons, recluses, heretics, monarchs, rivers, those who dwell on river-banks, carriage-makers, carpenters etc.